1. Field of the Invention
This invention relates to a mower comprising a frame equipped with a connecting device for connecting the frame to a motor vehicle, at least one harvesting mechanism equipped in particular with cutting elements and connected to the frame by a suspension device which allows a displacement in height of the harvesting mechanism relative to the frame, and a lightening device combined with the harvesting mechanism comprising at least one spring connected directly to the harvesting mechanism.
2. Description of the Related Art
A pulled mower comprising a frame which extends crosswise to the direction of advance at work is known. At each of its ends, this frame is equipped with a wheel by which it rests on the ground. In the median part, the frame is equipped with a tongue which makes it possible to hitch the mower to a tractor and which is connected to the frame by a joint with an axis directed at least approximately vertically. The frame supports a harvesting mechanism by a suspension device defining a deformable parallelogram. This device comprises two pairs of connecting rods each extending near one end of the frame, respectively of the harvesting mechanism. Moreover, a lightening device of the harvesting mechanism extends between the harvesting mechanism and the frame. This lightening device comprises two draw springs each extending near one end of the frame, respectively of the cutting mechanism, in front of the corresponding pair of connecting rods of the deformable parallelogram suspension device. Each draw spring is directly connected to the harvesting mechanism by a bolt going through a lug integral with the harvesting mechanism and screwed into a connecting piece integral with the spring. By screwing the bolt more or less tightly into the connecting piece of the spring, the spring is more or less extended, which makes it possible to adjust the lightening desired at the corresponding end of the harvesting mechanism. Because of the deformable parallelogram suspension device, the harvesting mechanism can be displaced in height relative to the frame, to adapt itself to the configurations of the soil and to pass above the obstacles that the soil can present. The lightening device makes it possible to reduce the pressure with which the harvesting mechanism rests on the ground, by transferring a part of the weight of the harvesting mechanism to the frame. Because of this device, the harvesting mechanism passes more easily above obstacles that the soil presents. Since the harvesting mechanism rests less heavily on the ground, a reduction of the power necessary to the displacement of the mower is also derived from it. In case the harvesting mechanism comprises a support beam extending under the cutting elements by supporting the latter and sliding over the ground, it finally makes it possible to reduce the risks of accumulations of earth at the front part of the support beam.
The advantage of the lightening device of this known mower resides in the fact that the springs are directly connected to the harvesting mechanism. This actually makes it possible for the lightening device to work with extremely short response times.
In practice, however, it was proven that this lightening device was not optimal. Actually, taking into account the usual production tolerances of the springs, variations in characteristics of the metal due to heat treatment, of the extent of the prestressing, etc., springs responding dimensionally to a given design can have characteristics which differ in appreciable proportions. Consequently, a problem occurs in that the two ends of the harvesting mechanism can rest with different pressures on the ground. The system of adjustment of the tension of each spring makes it possible theoretically to equalize the pressures with which the ends of the harvesting mechanism rest on the ground. This would require, however, a measuring device that the user generally does not have. Moreover, when one of the ends of the harvesting mechanism passes above an obstacle, the two ends of the harvesting mechanism also rest with different pressures on the ground.
In practice, it is therefore found that the harvesting mechanism is often very imperfectly lightened.